It is well known in the art to use air for corrosion prevention in a urea process wherein oxygen contained therein passivates the equipment metal surfaces. It is also well known that in most instances the CO.sub.2 feed supplied to a urea process contains hydrogen and nitrogen. Typically, air is added to the CO.sub.2 feed supplied to the urea reactor. In some urea processes the hydrogen contained in the CO.sub.2 feed is reacted with oxygen in the air injected into the process. In other processes the hydrogen remains in the process and is an inert which must be purged from the process along with nitrogen from the air and other inerts. In an integrated process, a portion of the high pressure air compressed for synthesis gas preparation in ammonia production is diverted for metal passivation in urea production. It can be seen that a large quantity of inerts in the reaction feed stream must then be purged from the reaction effluent stream.
A high pressure vapor purge stream removed from the urea synthesis reactor also contains unreacted carbon dioxide and ammonia. Such residuals are substantially absorbed as carbamate in a scrubber employing an aqueous carbamate wash and operating at the synthesis cycle pressure. Purge vapor removed from the high pressure scrubber comprising mostly nitrogen and residual ammonia is generally let down to a medium pressure absorber. The medium pressure absorber employs a plant condensate wash to reduce residual ammonia concentration in the purge vapor to a level suitable for venting to the atmosphere.
It would be advantageous in terms of energy and capital savings to avoid depressurization of the high pressure urea synthesis purge stream and the need for equipment required to remove residual ammonia for atmospheric disposal.